1. Field of the Invention
This invention relates generally to semiconductor processing, and, more particularly, methods and apparatus for atomic layer deposition processes.
2. Description of the Related Art
Atomic layer deposition is a technique for applying thin films to, for example, a semiconductor substrate. Although atomic layer deposition is a relatively new technology compared to, e.g. chemical vapor deposition, experimentation has shown that atomic layer deposition has an outstanding ability to form ultra-uniform thin deposition layers over complex topology. For example, atomic layer deposition processes have been used to deposit a one-atom-thick copper layer on a dielectric layer. For another example, a one-molecule-thick tantalum nitride barrier layer may be deposited on a low dielectric constant (low-K) dielectric film. Semiconductor devices formed using atomic layer deposition techniques may have length scales of 65-nanometers and below.
A typical atomic layer deposition process includes a sequence of gas flows. In one embodiment, a reactant precursor gas is provided to a reactor chamber in which a workpiece has been placed. For example, tri-methyl aluminum may be provided to the reactor chamber for about 0.5-10 seconds. Atoms or molecules in the first precursor gas form a saturated monolayer on the workpiece via chemisorption of the first precursor gas. A second precursor gas, e.g. a reducing and/or oxidizing gas, is then provided to the reactor chamber. For example, H2O, O3, or NH3 gases may be provided to the reactor chamber for 0.5-10 seconds. The atoms or molecules in the second precursor gas are also chemisorbed to form a first atomic or molecular layer from the saturated monolayer. The atomic layer deposition process may be repeated to form a layer of any desired thickness.
The high reactivity of the two precursor gases may result in gas phase nucleation when the reactant precursor gas and the reducing and/or oxidizing precursor gas are both present in the reactor chamber. Particles formed by the gas phase nucleation may contaminate the workpiece and/or the reactor chamber. To reduce the amount of gas phase nucleation and the resulting contamination, the reactant precursor gas is typically purged from the reactor chamber before the reducing and/or oxidizing precursor gas is introduced into the reactor chamber. For example, the first reactant gas may be purged by injecting an inert gas such as argon into the reactor chamber. The reducing and/or oxidizing precursor gas may also be purged before other gases are introduced.
The duration of the purge depends, at least in part, on the degree and kinetics of the physisorption on interior surfaces of the reactor chamber. The precursor gases may be adsorbed onto surfaces in the reactor chamber when they are introduced into the reactor chamber, and the adsorbed precursor gases may then be desorbed during the purge. The desorbed precursor gases may increase the concentration of precursor gases in the reactor chamber during the purge step and thereby increase the time required to purge the chamber. For example, the reactor chamber may be purged for about 2-10 seconds, or until the concentration of the reactant gas falls to about 1010 atoms/cc. Consequently, the throughput of the atomic layer deposition process is limited, at least in part, by the duration of the purge.
In one aspect of the instant invention, an apparatus is provided for performing an atomic layer deposition process. The apparatus includes a chamber adapted to receive a first precursor gas, at least one surface interior to the chamber, and an acoustic wave driver coupled to the at least one surface and adapted to drive acoustic waves along the interior surface.
In one aspect of the present invention, a method is provided for performing an atomic layer deposition process. The method includes providing a surface acoustic wave to at least one surface in a chamber, providing a first precursor gas to the chamber concurrent with providing the surface acoustic wave, and removing a portion of the first precursor gas from the chamber.